1. Technical Field
The present invention relates to an electrostatic charging member, an electrostatic charging device, a process cartridge and an image forming apparatus.
2. Related Art
Image forming apparatuses, notably printers and copiers, have come into widespread use in recent years, and technologies regarding various constituents of such image forming apparatuses have also diffused widely. Of image forming apparatuses, the image forming apparatus adopting electrophotography performs electrostatic charging of an image holding member by use of an electrostatic charging device, and thereby forms electrostatic latent images differing from their surroundings in electric potential on the electrostatically charged image holding member. The thus formed electrostatic latent images are developed with a developer containing toner, and eventually transferred to a recording material. Quite recently, a process cartridge into which constituents of an image forming apparatus, including an image holding member and an electrostatic charging device, are integrated has dominated the market. By incorporating such a process cartridge into an image forming apparatus, the image forming apparatus can be equipped with a plurality of constituents, including an image holding member and an electrostatic charging device, as a single unit, and so maintenance management of the image forming apparatus becomes easy.
Electrostatic charging devices are devices having the function of charging electrostatically image holding members, and roughly classified into two types of charging devices, namely charging devices according to a contact charging method, which are brought into direct contact with image holding members and perform electrostatic charging of the image holding members, and charging devices according to a non-contact charging method, which are not brought into direct contact with image holding members but perform electrostatic charging of the image holding members by generating corona discharge or the like in proximity of the image holding members. In the charging devices according to a non-contact charging method, there may be cases where products such as ozone and nitrogen oxides are evolved secondarily by electric discharge. Therefore, recent years have seen a growth in the number of charging devices adopting the contact charging method.
The electrostatic charging device according to a contact charging method is equipped with an electrostatic charging member such as an electrostatic charging roll, which is brought into direct contact with the surface of an image holding member and made to rotate in synchronization with movement of the image holding member's surface, thereby giving electrostatic charges to the image holding member. The electrostatic charging roll is made up of, e.g., a base material and an elastic conducting layer formed around the peripheral surface of the base material.